Effects of plant community structural characteristics on carbon sequestration in urban green spaces

The structural characteristics of plant communities in urban green spaces have a significant impact on their carbon sequestration function. In this study, comprehensive data were collected from 106 plant communities (each 20 m × 20 m) in Zhengzhou Green Expo Park. We assessed aboveground and soil carbon storage, alongside maintenance carbon emissions, to quantify carbon dynamics. Our primary objective was to establish a statistical model that correlates the structural attributes of plant communities with their total annual carbon sequestration. This model aims to provide a quantitative framework for optimizing community structures to maximize carbon sequestration in urban green spaces. The results showed that density and coverage were significantly and positively correlated with aboveground and soil carbon stocks. Density and mean height were significantly and positively correlated with maintenance carbon emissions. Density played a key structural role in regulating the total carbon sequestration of the plant communities, being 27.24 times more effective than coverage. The total annual carbon sequestration of the plant community reached an optimal value of 327.67 kg CO2-eq/y-1 at a density and cover of 0.15 and 1, respectively. This study provides valuable data for increasing the carbon sink ability of urban green spaces through plant structure regulation and supporting low-carbon development strategies in urban management.

A comparison between different patient groups for diabetes management during phases of the COVID-19 pandemic: a retrospective cohort study in Ontario, Canada

BACKGROUND

With the onset of the COVID-19 pandemic and the large uptake in virtual care in primary care in Canada, the care of patients with type 2 diabetes has been greatly affected. This includes decreased in-person visits, laboratory testing and in-person assessments such as blood pressure (BP). No studies have investigated if these changes persisted with pandemic progression, and it is unclear if shifts impacted patient groups uniformly. The purpose of this paper was to examine changes in diabetes care pre, early, and later pandemic across different patient groups.

METHODS

A repeated cross-sectional design with an open cohort was used to investigate diabetes care in adults with type 2 diabetes for a 6-month interval from March 14 to September 13 over three consecutive years: 2019 (pre-pandemic period), 2020 (early pandemic period), and 2021 (later pandemic period). Data for this study were abstracted from the University of Toronto Practice-Based Research Network (UTOPIAN) Data Safe Haven, a primary care electronic medical records database in Ontario, Canada. Changes in diabetes care, which included primary care total visits, in-person visits, hemoglobin A1c (HbA1c) testing, and BP measurements were evaluated across the phases of the pandemic. Difference in diabetes care across patient groups, including age, sex, income quintile, prior HbA1c levels, and prior BP levels, were assessed.

RESULTS

A total of 39,401 adults with type 2 diabetes were included in the study. Compared to the 6-month pre-pandemic period, having any in-person visits decreased significantly early pandemic (OR = 0.079 (0.076-0.082)), with a partial recovery later pandemic (OR = 0.162 (95% CI: 0.157-0.169). Compared to the pre-pandemic period, there was a significant decrease early pandemic for total visits (OR = 0.486 (95% CI: 0.470-0.503)), HbA1c testing (OR = 0.401 (95% CI: 0.389-0.413)), and BP measurement (OR = 0.121 (95% CI: 0.116-0.125)), with partial recovery later pandemic.

CONCLUSIONS

All measures of diabetes care were substantially decreased early pandemic, with a partial recovery later pandemic across all patient groups. With the increase in virtual care due to the COVID-19 pandemic, diabetes care has been negatively impacted over 1-year after pandemic onset.

Policy stringency and the spread of COVID-19: The moderating role of culture and its implications on first responses

There has been a noticeable variance between countries in the growth rate of COVID-19 since the start of the pandemic. Researchers attempted to understand this variance from two primary perspectives: the policies implemented to curb the spread of the virus [1] and the cross-country cultural differences [2]. However, little research to date has looked at the joint effects of policy responses and national culture. We argue that the effectiveness of restrictive policies depends on cultural values. Specifically, when policies are non-mandatary, cultural values influence people's voluntary adherence to these policies, and hence, the spread of COVID-19. We analyzed the growth data in daily new cases across 78 countries, focusing on the joint impact of containment policies and cultural values. We found that although policy responses (i.e., containment policies) significantly predicted the spread rate of COVID-19 over time, their effects were moderated by cultural variables as well. Implications for policymaking are discussed.

Complex chronic conditions among children born to women with schizophrenia

PURPOSE

Maternal schizophrenia is linked to complications in offspring near the time of birth. Whether there is also a higher future risk of the child having a complex chronic condition (CCC) - a pediatric condition affecting any bodily system expected to last at least 12 months that is severe enough to require specialty care and/or a period of hospitalization - is not known.

METHODS

In this population-based health administrative data cohort study (Ontario, Canada, 1995-2018), the risk for CCC was compared in 5066 children of women with schizophrenia (the exposed) vs. 2,939,320 unexposed children. Adjusted hazard ratios (aHR) were generated for occurrence of any CCC, by CCC category, and stratified by child sex, and child prematurity.

RESULTS

CCC was more frequent in the exposed (7.7 per 1000 person-years [268 children]) than unexposed (4.2 per 100 person-years [124,452 children]) - an aHR of 1.25 (95% CI 1.10-1.41). aHRs were notably higher in 5 of 9 CCC categories: neuromuscular (1.73, 1.28-2.33), cardiovascular (1.94, 1.64-2.29), respiratory (1.83, 1.32-2.54), hematology/immunodeficiency (2.24, 1.24-4.05) and other congenital or genetic defect (1.59, 1.16-2.17). The aHR for CCC was more pronounced among boys (1.32, 1.13-1.55) than girls (1.16, 0.96-1.40), and of similar magnitude in term (1.22, 1.05-1.42) and preterm infants (1.18, 0.95-1.46).

CONCLUSIONS

The risk for a CCC appears to be higher in children born to women with schizophrenia. This finding introduces opportunities for targeted preconception counselling, optimization of maternal risk factors, and intervention to support a vulnerable parent population who will experience unique challenges caring for a child with CCCs.

The association of stroke rate with low density lipoprotein and statin exposure in patients with atrial fibrillation (AF)

Background

There are limited data on the association between cholesterol levels and stroke risk in atrial fibrillation (AF).

Objective

To quantify the association of stroke rate in AF with low-density lipoprotein (LDL) levels and statin use.

Methods

Using linked administrative databases in Ontario, Canada, we conducted a population-based retrospective cohort study of patients aged ≥66 years, diagnosed with AF between 2009–2019. We used cause-specific hazard regression to determine the association of statin use with stroke rate. We developed a second cause-specific regression model for patients with at least one lipid profile measurement in the year before AF diagnosis to study the association of LDL levels with stroke rate, while adjusting for statin use. LDL levels were modeled using restricted cubic splines (RCS). Both models were adjusted for age, sex, heart failure, hypertension, diabetes, stroke or transient ischemic attack, and vascular disease at baseline, plus anticoagulation as a time-varying covariate.

Results

We studied 261,659 qualifying patients (median age 78 years, 49% female), of whom 3,954 (1.5%) developed a stroke during one-year follow-up. A total of 142,834 (54.6%) patients were treated with statins and 145,775 (55.7%) had lipid measurements before AF diagnosis. The adjusted RCS analyses (see Figure) indicated increasing hazard ratios (HRs) for stroke with increasing low-density lipoprotein (LDL) values above 1.5mmol/L. Statin use was associated with a lower stroke rate relative to non-users (hazard ratio 0.87, 95% confidence interval 0.81–0.93, p-value <0.0001).

Conclusion

LDL levels above 1.5mmol/L were independently associated with higher stroke rates in patients with AF, while statins were associated with lower stroke rates independent of anticoagulation. This suggests that LDL measurements may improve stroke risk stratification in AF, while statins may offer an underutilized pathway to lower stroke risk in AF.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): 1) Heart and stroke foundation of Canada HR for Stroke and LDL level

Antibiotics-induced intestinal dysbacteriosis caused behavioral alternations and neuronal activation in different brain regions in mice

Antibiotics affect gut microbial composition, leading to Gut-Brain-Axis imbalance and neurobehavioral changes. However, the intestinal dysbacteriosis associated behavior changes are not consistently reported. It is not clear whether these changes are transient or permanent. The neuroprotective effect of probiotics against intestinal dysbacteriosis induced alternations needs to be determined either. In the present study, oral antibiotic mixture including Ampicillin, Streptomycin, and Clindamycin was utilized to induce intestinal dysbacteriosis in mice. Antibiotics application triggered mechanical allodynia in von frey test and spontaneous pain in open field test. It also resulted in increased anxiety and depressive-like behaviors and damaged spatial memory performance. After application of probiotics, the mechanical allodynia and spontaneous pain were alleviated significantly. The anxiety behaviors, depressive-like behaviors and recognitive performance were ameliorative as well. By using Fos protein as a marker, it is found that the sensory, emotion and memory related brain regions were activated in mice with intestinal dysbacteriosis. Our study is not only helpful for enriching our basic knowledge for understanding the changed pain responses and related brain disorders in antibiotics-induced dysbacteriosis mice, but also beneficial for providing a more comprehensive mechanistic explanation for the regulation of antibiotics and probiotics on gut microbiota and relevant alternations in animal neurological behaviors.

P3518Men with heart failure have higher readmission rates: a closer review of sex and gender based analyses

Background

There has been increased attention on reducing hospital readmission rates. However, little is known about any difference in readmission rates in heart failure by sex, although evidence exists demonstrating differences in the etiology of heart failure. As a result, strategies to optimize readmission reduction programs and care strategies for women and men remain unclear.

Purpose

(1) To identify studies examining readmission rates according to sex, and (2) to provide a qualitative overview of possible considerations for the impact of sex or gender.

Methods

A scoping protocol was developed using the Arksey and O'Malley framework and the Joanna Briggs Institute methodology. Our search strategy was reviewed according to the peer-review of electronic search strategy (PRESS) checklist. Full text articles published between 2002 and 2017 and drawn from multiple databases (i.e. MEDLINE, EMBASE), grey literature (i.e. National Technical Information, Duck Duck Go), and experts were consulted for additional articles. Screening criteria were established a priori. Once an acceptable inter-rater agreement was established at 80% by two independent reviewers, articles were screened for potential eligibility. A descriptive analytical method was employed to chart primary research articles. Articles were considered relevant if the cohort consisted of adult heart failure patients who were readmitted after an index hospitalization and a sex/gender-based analysis was performed.

Results

The literature search yielded 5887 articles, of which 746 underwent full text assessment for eligibility. Of 164 eligible articles, 34 studies addressed the primary outcome, 103 studies considered sex differences as a secondary outcome and 25 studies included disaggregated data for sex but no subsequent interaction was reported. Good inter-rater agreement was reached: 83% for title and abstract screening; 88% for full text review; kappa: 0.69 (95% CI: 0.526–0.851). Twelve of 34 studies included for the primary outcome reported higher readmission rates for men compared to five studies reporting higher readmission rates for women. However, there were differential readmission rates that were dependent on duration of follow-up. Women were more likely to experience higher readmission rates than men when time to event was less than one year. Readmission rates for men were higher when follow-up was longer than one year.

Conclusion

Sex differences in readmission rates were dependent on follow up time. Most studies used composite outcomes and had short times to event, which may mask underlying effects of sex on readmission.

Acknowledgement/Funding

Ontario SPOR Support Unit

The excitatory synaptic transmission of the nucleus of solitary tract was potentiated by chronic myocardial infarction in rats

Angina pectoris is a common clinical symptom that often results from myocardial infarction. One typical characteristic of angina pectoris is that the pain does not match the severity of the myocardial ischemia. One possible explanation is that the intensity of cardiac nociceptive information could be dynamically regulated by certain brain areas. As an important nucleus for processing cardiac nociception, the nucleus of the solitary tract (NTS) has been studied to some extent. However, until now, the morphological and functional involvement of the NTS in chronic myocardial infarction (CMI) has remained unknown. In the present study, by exploring left anterior descending coronary artery ligation surgery, we found that the number of synaptophysin-immunoreactive puncta and Fos-immunoreactive neurons in the rat NTS two weeks after ligation surgery increased significantly. Excitatory pre- and postsynaptic transmission was potentiated. A bath application of a Ca²⁺ channel inhibitor GABApentin and Ca²⁺ permeable AMPA receptor antagonist NASPM could reverse the potentiated pre- and postsynaptic transmission, respectively. Meanwhile, rats with CMI showed significantly increased visceral pain behaviors. Microinjection of GABApentin or NASPM into the NTS decreased the CMI-induced visceral pain behaviors. In sum, our results suggest that the NTS is an important area for the process of cardiac afference in chronic myocardial infarction condition.

Fracture risk assessment after BMD examination: whose job is it, anyway?

Fracture risk assessments on bone mineral density reports guide family physicians' treatment decisions but are subject to inaccuracy. Qualitative analysis of interviews with 22 family physicians illustrates their pervasive questioning of reported assessment accuracy and independent assumption of responsibility for assessment. Assumption of responsibility is common despite duplicating specialists' work.

INTRODUCTION

Fracture risk is the basis for recommendations of treatment for osteoporosis, but assessments on bone mineral density (BMD) reports are subject to known inaccuracies. This creates a complex situation for referring physicians, who must rely on assessments to inform treatment decisions. This study was designed to broadly understand physicians' current experiences with and preferences for BMD reporting; the present analysis focuses on their interpretation and use of the fracture risk assessments on reports, specifically

METHODS

A qualitative, thematic analysis of one-on-one interviews with 22 family physicians in Ontario, Canada was performed.

RESULTS

The first major theme identified in interview data reflects questioning by family physicians of reported fracture risk assessments' accuracy. Several major subthemes related to this included questioning of: 1) accuracy in raw bone mineral density measures (e.g., g/cm(2)); 2) accurate inclusion of modifying risk factors; and 3) the fracture risk assessment methodology employed. A second major theme identified was family physicians' independent assumption of responsibility for risk assessment and its interpretation. Many participants reported that they computed risk assessments in their practice to ensure accuracy, even when provided with assessments on reports.

CONCLUSIONS

Results indicate family physicians question accuracy of risk assessments on BMD reports and often assume responsibility both for revising and relating assessments to treatment recommendations. This assumption of responsibility is common despite the fact that it may duplicate the efforts of reading physicians. Better capture of risk information on BMD referrals, quality control standards for images and standardization of risk reporting may help attenuate some inefficiency.

The risk of falls on initiation of antihypertensive drugs in the elderly

SUMMARY

Antihypertensive drugs are associated with an immediate increased falls risk in elderly patients which was significant during the first 14 days after receiving a thiazide diuretic, angiotensin-converting enzyme inhibitor, angiotensin II receptor blocker, calcium channel blocker, or beta-adrenergic blocker. Fall prevention strategies during this period may prevent fall-related injuries.

INTRODUCTION

The purpose of this study is to evaluate if initiation of the common antihypertensive drugs is associated with the occurrence of falls.

METHODS

This population-based self-controlled case series study used healthcare administrative databases to identify new users of antihypertensive drugs in the elderly aged 66 and older living in Ontario, Canada who suffered a fall from April 1, 2000 to March 31, 2009. The risk period was the first 45 days following antihypertensive therapy initiation, further subdivided into 0-14 and 15-44 days with control periods before and after treatment in a 450-day observation period. We calculated the relative incidence (incidence rate ratio, IRR), defined as the rate of falls in the risk period compared to falls rate in the control periods.

RESULTS

Of the 543,572 new users of antihypertensive drugs among community-dwelling elderly, 8,893 experienced an injurious fall that required hospital care during the observation period. New users had a 69 % increased risk of having an injurious fall during the first 45 days following antihypertensive treatment (IRR = 1.69; 95 % CI, 1.57-1.81). This finding was consistent for thiazide diuretics, angiotensin-converting enzyme inhibitors, calcium channel blockers, and beta-adrenergic blockers but not angiotensin II receptor antagonists. There was also an increased falls risk during the first 14 days of antihypertensive drug initiation (IRR = 1.94; 95 % CI, 1.75-2.16), which was consistent for all antihypertensive drug classes.

CONCLUSIONS

This study suggests that initiation of antihypertensive drugs is a risk factor for falls in the elderly. Fall prevention strategies during this period may reduce injuries.

Identifying cases of congestive heart failure from administrative data: a validation study using primary care patient records

INTRODUCTION

To determine if using a combination of hospital administrative data and ambulatory care physician billings can accurately identify patients with congestive heart failure (CHF), we tested 9 algorithms for identifying individuals with CHF from administrative data.

METHODS

The validation cohort against which the 9 algorithms were tested combined data from a random sample of adult patients from EMRALD, an electronic medical record database of primary care physicians in Ontario, Canada, and data collected in 2004/05 from a random sample of primary care patients for a study of hypertension. Algorithms were evaluated on sensitivity, specificity, positive predictive value, area under the curve on the ROC graph and the combination of likelihood ratio positive and negative.

RESULTS

We found that that one hospital record or one physician billing followed by a second record from either source within one year had the best result, with a sensitivity of 84.8% and a specificity of 97.0%.

CONCLUSION

Population prevalence of CHF can be accurately measured using combined administrative data from hospitalization and ambulatory care.

Myocardial infarction and the validation of physician billing and hospitalization data using electronic medical records

OBJECTIVE

Population-based identification of patients with a myocardial infarction is limited to patients presenting to hospital with an acute event. We set out to determine if adding physician billing data to hospital discharge data would result in an accurate capture of patients who have had a myocardial infarction.

METHODS

We performed a retrospective chart abstraction of 969 randomly selected adult patients using data abstracted from primary care physicians on an electronic medical record in Ontario, Canada, as the reference standard.

RESULTS

An algorithm of 3 physician billings in a one-year period with at least one being by a specialist or within a hospital or emergency room plus one hospital discharge abstract performed with a sensitivity of 80.4% (95% CI: 69.5-91.3), specificity of 98.0% (95% CI: 97.1-98.9), positive predictive value of 69.5% (95% CI: 57.7-81.2), negative predictive value of 98.9% (95% CI: 98.2% to 99.6%) and kappa statistic of 0.73 (95% CI: 0.63-0.83).

CONCLUSION

Using a combination of hospital discharge abstracts and physician billing data may be the best way of assessing trends of MI occurrence over time since it increases the capture of MI beyond those patients who have been hospitalized.

Structure determination by restrained molecular dynamics using NMR pseudocontact shifts as experimentally determined constraints

The structure of a DNA octamer d(TTGGCCAA)(2) complexed to chromomycin-A(3) and a single divalent cobalt ion has been solved by using the pseudocontact shifts due to the unpaired electrons on the cobalt. A protocol was developed and critically evaluated for using the pseudocontact shifts in structure determination. The pseudocontact shifts were input as experimental restraints in molecular dynamics simulations with or without NOE constraints. Both the magnitude and orientation of the susceptibility anisotropy tensor required for the shift calculations were determined during the simulations by iterative refinement. The pseudocontact shifts could be used to define the structure to a very high precision and accuracy compared with a corresponding NOE-determined structure. Convergence was obtained from different starting structures and tensors. A structure determination using both NOE's and pseudocontact shifts revealed a general agreement between the two data sets. However, some evidence for a discrepancy between NOE's and pseudocontact shifts was observed in the backbone and terminal base pairs of the DNA. Violations in shift or NOE restraints remaining in the final structures were examined and may be a reflection of motional averaging of the constraints and evidence for flexibility. This work demonstrates that pseudocontact shifts are a powerful tool for NMR structure determination.

Use of beta-blockers for uncomplicated hypertension in the elderly: a cause for concern

Beta-blockers are less beneficial than other antihypertensive drugs in the elderly with hypertension. All elderly patients in Ontario, Canada (population over 3.5 million elderly) without co-morbidities who were first treated for hypertension with a beta-blocker were studied in a retrospective population-based cohort study (1994-2002) to determine the characteristics of those prescribed beta-blockers. Of the 194,761 patients in our cohort, 25 485 (13%) were prescribed a beta-blocker as their first antihypertensive agent. On multivariate analysis, factors significantly associated with being prescribed a beta-blocker as first-line therapy included male sex (adjusted odds ratio (OR) 1.06 [95% CI 1.03-1.09] vs women), younger age (adjusted OR 1.67 [95% CI 1.55-1.79] for patients aged 66-69 vs those aged 85 or older), residence in a long-term care facility (adjusted OR 1.19 [95% CI 1.04-1.35] vs living in the community) and lower socioeconomic status (adjusted OR 1.07 [95% CI 1.02-1.12], for lowest quintile vs highest quintile). Patients with diabetes were substantially less likely to be prescribed beta-blockers (adjusted OR 0.42 [95% CI 0.40-0.44]). Greater efforts are required to educate physicians to select other drugs for initial therapy in older patients with uncomplicated hypertension.

Progressive trends in the prevalence of benzodiazepine prescribing in older people in Ontario, Canada

OBJECTIVES

The extensive use of benzodiazepines has been a concern of healthcare providers and policy makers in Canada and around the world. The purpose of this study was to examine temporal trends in benzodiazepine prescriptions dispensed in older people from 1993-1998.

DESIGN

Retrospective population-based cross-sectional study using administrative databases.

SETTING

Ontario, Canada.

PARTICIPANTS

The over 1 million residents of Ontario age 65 and older covered by the provincial universal drug benefit program.

MEASUREMENTS

The main outcome measures were the prevalence, overall and with respect to age and gender, of benzodiazepine prescriptions dispensed and the ratio of the number of people to whom short- versus long-acting benzodiazepine prescriptions were dispensed in each study year. The annual rates of switching to other psychotropic agents were examined for those patients that discontinued filling benzodiazepine prescriptions.

RESULTS

The annual prevalence of benzodiazepine prescriptions dispensed decreased consistently over time (25.1% in 1993 to 22.5% in 1998; P < .001). Benzodiazepine dispensing prevalence increased with increasing age (approximately 20% of those age 65 to 69 to approximately 30% of those age > or =85; P < .001) and more females than males received the medication (relative risk = 1.50, 95% confidence interval = 1.49-1.51). The ratio of short- to long-acting benzodiazepine prescriptions filled increased over time (3.6 in 1993 to 5.8 in 1998; P < .001), in line with guideline recommendations. Rates of switching to antidepressants increased over time (8.5% in 1993 to 10.2% in 1998; P < .001), whereas switching to barbiturates was consistently low (0.12%; P = .403).

CONCLUSION

The prevalence of benzodiazepine therapy for older people in Ontario has steadily declined between 1993 and 1998. There is a trend of dispensing relatively more short-acting than long-acting benzodiazepines and of replacing benzodiazepines with antidepressants in older people without a remarkable increase in barbiturate consumption. These findings suggest that, without undue regulation, physicians are making progress in the prescribing of benzodiazepine therapy on the basis of current knowledge available.

Proton pump inhibitors. Compliance with a mandated step-up program

OBJECTIVE

To assess compliance with a step-up approach to proton pump inhibitor (PPI) therapy before implementation of a new provincial policy to promote histamine-type 2 receptor antagonist (H2RA) use before PPI therapy.

DESIGN

Population-based, retrospective, open cohort study using prescribing and medical procedure data from January 1, 1995, to April 30, 1999.

SETTING

Health administration databases for the universal health care system in Ontario.

PARTICIPANTS

Approximately 1.4 million residents of Ontario older than 65 years.

MAIN OUTCOME MEASURES

Proportion of patients who received a trial of H2RA therapy or gastrointestinal diagnostic testing 12 months before starting PPI therapy in 1996.

RESULTS

Among the 25,870 patients who met study criteria in 1996, about 63% had received H2RAs 12 months before starting PPI therapy and 73% had had a trial of H2RAs or gastrointestinal diagnostic testing. Repeat analysis for January through April 1999, following the new policy implementation, showed that about 72% of patients had had a trial of H2RAs within 12 months of starting PPI therapy.

CONCLUSION

A modest gain (9%) in compliance with using H2RA therapy within 12 months before starting PPI therapy was seen following introduction of the step-up intervention. In future, costs and benefits of potential interventions should be carefully considered before implementing new policies.

Postmenopausal estrogen replacement therapy and increased rates of cholecystectomy and appendectomy

BACKGROUND

Several studies have indicated that estrogen may prime inflammatory and nociceptive pathways, leading to symptoms that mimic cholecystitis. We set out to confirm the relation between recent estrogen use and cholecystectomy in postmenopausal women and to test the novel hypothesis that a similar relation exists for appendectomy.

METHODS

We developed a retrospective cohort using prescribing and surgical procedure information from health administrative databases for approximately 800,000 female residents of Ontario who were over 65 years of age between July 1, 1993, and Mar. 31, 1998. We compared the incidence of cholecystectomy and appendectomy among women recently prescribed estrogen replacement therapy, levothyroxine and dihydropyridine calcium-channel antagonists (DCCA) using age-adjusted Cox proportional hazards models. Patients were followed for a mean of 540 (standard deviation [SD] 449) days.

RESULTS

Compared with women taking DCCA, those who had recently begun taking estrogen were significantly more likely to undergo cholecystectomy (age-adjusted risk ratio [aRR] 1.9, 95% confidence interval [CI] 1.6-2.2) and appendectomy (aRR 1.8, 95% CI 1.1-3.0). No significant difference in either outcome measure was found between the levothyroxine users and the DCCA users.

INTERPRETATION

This study identifies an increased risk of cholecystectomy and appendectomy among postmenopausal women who have recently begun estrogen replacement therapy.

Molecular dynamics simulations of supported phospholipid/alkanethiol bilayers on a gold(111) surface

Molecular dynamics simulations have been used to investigate the structure of hybrid bilayers (HB) formed by dipalmitoylphosphatidylcholine (DPPC) lipid monolayers adsorbed on a hydrophobic alkanethiol self-assembled monolayer (SAM). The HB system was studied at 20 degrees C and 60 degrees C, and the results were compared with recent neutron reflectivity measurements (Meuse, C. W., S. Krueger, C. F. Majkrzak, J. A. Dura, J. Fu, J. T. Connor, and A. L. Plant. 1998. Biophys. J. 74:1388) and previous simulations of hydrated multilamellar bilayers (MLB) of DPPC (Tu, K., D. J. Tobias, and M. L. Klein. 1995. Biophys. J. 69:2558; and 1996. 70:595). The overall structures of the HBs are in very good agreement with experiment. The structure of the SAM monolayer is hardly perturbed by the presence of the DPPC overlayer. The DPPC layer presents characteristics very similar to the MLB gel phase at low temperature and to the liquid crystal phase at high temperature. Subtle changes have been found for the lipid/water interface of the HBs compared to the MLBs. The average phosphatidylcholine headgroup orientation is less disordered, and this produces changes in the electric properties of the HB lipid/water interface. These changes are attributed to the fact that the aqueous environment of the lipids in these unilamellar films is different from that of MLB stacks. Finally, examination of the intramolecular and whole-molecule dynamics of the DPPC molecules in the fluid phase HB and MLB membranes revealed that the reorientations of the upper part of the acyl chains (near the acyl ester linkage) are slower, the single molecule protrusions are slightly damped, and the lateral rattling motions are significantly reduced in the HB compared with the MLB.

Analysis of simulated NMR order parameters for lipid bilayer structure determination

The conventional formula for relating CD2 average order parameters <Sn> to average methylenic travel <Dn> is flawed when compared to molecular dynamics simulations of dipalmitoylphosphatidylcholine. Inspired by the simulated probability distribution functions, a new formula is derived that satisfactorily relates these quantities. This formula is used to obtain the average chain length <LC>, and the result agrees with the direct simulation result for <LC>. The simulation also yields a hydrocarbon thickness 2<DC>. The result <LC> = <DC> is consistent with a model of chain packing with both early chain termination and partial interdigitation of chains from opposing monolayers. The actual simulated area per lipid <A> is easily obtained from the order parameters. However, when this method is applied to NMR order parameter data from dimyristoylphosphatidylcholine, the resulting <A> is 10% larger than the currently accepted value.

Constant-pressure molecular dynamics investigation of cholesterol effects in a dipalmitoylphosphatidylcholine bilayer

We report a 1.4-ns constant-pressure molecular dynamics simulation of cholesterol at 12.5 mol% in a dipalmitoylphosphatidylcholine (DPPC) bilayer at 50 degrees C and compare the results to our previous simulation of a pure DPPC bilayer. The interlamellar spacing was increased by 2.5 A in the cholesterol-containing bilayer, consistent with x-ray diffraction results, whereas the bilayer thickness was increased by only 1 A. The bilayer/water interface was more abrupt because the lipid headgroups lie flatter to fill spaces left by the cholesterol molecules. This leads to less compensation by the lipid headgroups of the oriented water contribution to the membrane dipole potential and could explain the experimentally observed increase in the magnitude of the dipole potential by cholesterol. Our calculations suggested that 12.5 mol% cholesterol does not significantly affect the conformations and packing of the hydrocarbon chains and produces only a slight reduction in the empty free volume. However, cholesterol has a significant influence on the subnanosecond time scale lipid dynamics: the diffusion constant for the center-of-mass "rattling" motion was reduced by a factor of 3, and the reorientational motion of the methylene groups was slowed along the entire length of the hydrocarbon chains.

Effects of anesthetics on the structure of a phospholipid bilayer: molecular dynamics investigation of halothane in the hydrated liquid crystal phase of dipalmitoylphosphatidylcholine

We report the results of constant temperature and pressure molecular dynamics calculations carried out on the liquid crystal (Lalpha) phase of dipalmitoylphosphatidylcholine with a mole fraction of 6.5% halothane (2-3 MAC). The present results are compared with previous simulations for pure dipalmitoylphosphatidylcholine under the same conditions (Tu et al., 1995. Biophys. J. 69:2558-2562) and with various experimental data. We have found subtle structural changes in the lipid bilayer in the presence of the anesthetic compared with the pure lipid bilayer: a small lateral expansion is accompanied by a modest contraction in the bilayer thickness. However, the overall increase in the system volume is found to be comparable to the molecular volume of the added anesthetic molecules. No significant change in the hydrocarbon chain conformations is apparent. The observed structural changes are in fair agreement with NMR data corresponding to low anesthetic concentrations. We have found that halothane exhibits no specific binding to the lipid headgroup or to the acyl chains. No evidence is obtained for preferential orientation of halothane molecules with respect to the lipid/water interface. The overall dynamics of the lipid-bound halothane molecules appears to be reminiscent of that of other small solutes (Bassolino-Klimas et al., 1995. J. Am. Chem. Soc. 117:4118-4129).

Cellulitis and myositis caused by Agrobacterium radiobacter and Haemophilus parainfluenzae after influenza virus vaccination

Agrobacterium radiobacter is a gram-negative aerobic bacillus that has been reported as a cause of disease only 36 times in the literature. More than half of the patients (25) have had bacteremia. Peritonitis, urinary tract infection, endocarditis, and one case of cellulitis associated with bacteremia have also been reported. Infection is often associated with immunosuppression and the presence of a plastic foreign body, such as central venous catheters, nephrostomy tubes, intraperitoneal catheters, and prosthetic cardiac valves. We present apparently the first case of A radiobacter causing myositis after influenza virus vaccination.

Molecular dynamics investigation of the structure of a fully hydrated gel-phase dipalmitoylphosphatidylcholine bilayer

We report the results of a constant pressure and temperature molecular dynamics simulation of a gel-phase dipalmitoylphosphatidylcholine bilayer with nw = 11.8 water molecules/lipid at 19 degrees C. The results of the simulation were compared in detail with a variety of x-ray and neutron diffraction data. The average positions of specific carbon atoms along the bilayer normal and the interlamellar spacing and electron density profile were in very good agreement with neutron and x-ray diffraction results. The area per lipid and the details of the in-plane hydrocarbon chain structure were in excellent agreement with wide-angle x-ray diffraction results. The only significant deviation is that the chains met in a pleated arrangement at the bilayer center, although they should be parallel. Novel discoveries made in the present work include the observation of a bimodal headgroup orientational distribution. Furthermore, we found that there are a significant number of gauche conformations near the ends of the hydrocarbon chains and, in addition to verifying a previous suggestion that there is partial rotational ordering in the hydrocarbon chains, that the two chains in a given molecule are inequivalent with respect to rotations. Finally, we have investigated the lipid/water interface and found that the water penetrates beneath the headgroups, but not as far as the carbonyl groups, that the phosphates are strongly hydrated almost exclusively at the nonesterified oxygen atoms, and that the hydration of the ammonium groups is more diffuse, with some water molecules concentrated in the grooves between the methyl groups.

Constant pressure and temperature molecular dynamics simulation of a fully hydrated liquid crystal phase dipalmitoylphosphatidylcholine bilayer

We report a constant pressure and temperature molecular dynamics simulation of a fully hydrated liquid crystal (L alpha) phase bilayer of dipalmitoylphosphatidylcholine at 50 degrees C and 28 water molecules/lipid. We have shown that the bilayer is stable throughout the 1550-ps simulation and have demonstrated convergence of the system dimensions. Several important aspects of the bilayer structure have been investigated and compared favorably with experimental results. For example, the average positions of specific carbon atoms along the bilayer normal agree well with neutron diffraction data, and the electron density profile is in accord with x-ray diffraction results. The hydrocarbon chain deuterium order parameters agree reasonably well with NMR results for the middles of the chains, but the simulation predicts too much order at the chain ends. In spite of the deviations in the order parameters, the hydrocarbon chain packing density appears to be essentially correct, inasmuch as the area/lipid and bilayer thickness are in agreement with the most refined experimental estimates. The deuterium order parameters for the glycerol and choline groups, as well as the phosphorus chemical shift anisotropy, are in qualitative agreement with those extracted from NMR measurements.

The effect of posterior element resection on the stress distribution in the lumbar spine

A three-dimensional finite element model of the lumbar motion segment was used to predict the stress distribution in lumbar spine with posterior element resection. It was shown that the stress level in all parts of the lumbar spine was elevated although the stress distribution remained unchanged. The authors concluded that the posterior element resection in lumbar surgery should be avoided as much as possible.

The stress distribution of the lumbar spine and disc degeneration

A three-dimensional finite element model of the lumbar motion segment was developed to study the effect of disc degeneration upon stress distribution in the lumbar spine. The results showed that after degeneration of the intervertebral disc, the stress distribution and load transmission of the lumbar spine are significantly changed. It is concluded that these changes provide a biomechanical basis for understanding the etiology of spinal canal stenosis and nerve root entrapment.

Stress distribution and bone density in the lumbar spine

The stress distribution of the lumbar spine was analyzed with a mechanical model of the lumbar motion segment constructed by a three-dimensional finite element method, and the results were compared with the corresponding bone density represented by the value of CT. The results showed that the stress levels in the various parts of the lumbar spine were closely related to the CT values. The authors conclude that the dynamic balance of bone growth is maintained in large part by mechanical stress.